Assertions in a document may be associated with one or more citations to other documents, e.g., as authorities intended to support the respective assertions they are associated with. It may be desirable, however, to provide tools to help judge whether the cited documents do in fact support the associated assertions. Moreover, in some fields, the strength of support that a cited document may provide may change over time; for example, legal authority may be overruled or otherwise altered. It may therefore be desirable to determine the continued vitality of the cited document as support for some or all of the propositions that it may have asserted.